Load selectors of that kind belong to on-load tap changers (in abbreviation OLTC) and are widely known and conventional in the prior art. They serve for uninterrupted switching over between different winding taps of tapped transformers.
In general, on-load tap changers are actuated by a motor drive for switching over. A drive output or input shaft that draws up a force-storing unit is moved by the motor drive. When the force-storing unit is completely drawn up, i.e. stressed, it is unlatched, abruptly releases its energy and actuates, in a space of milliseconds (ms), a load changeover switch insert that then executes a specific switching sequence during the load changeover. In that case, different control contacts, also called switch contacts, and resistance contacts are then actuated in a specific time sequence. The control contacts serve for direct connection of the respective winding tap with the load diverter and the resistance contacts for temporary connection, i.e. bridging over, by means of one or more switching-over resistances. With advantage, vacuum interrupters (vacuum switching cells) are used as switching elements for the load changeover. This is due to the fact the use of vacuum interrupters for the load changeover prevents formation of arcs in the oil and thus oil contamination of the load changeover switch oil, such as described in, for example German Patent Specifications DE 195 10 809 C1 and DE 40 11 019 C1 as well as German published specifications DE 42 31 353 A1 and DE 10 2007 004 530 A1.
It is known from the prior art to arrange a plurality of vacuum interrupters in the same sense and upright on contact supports or contact housings of a load selector. In that case, by the term “same sense” there is meant in the context of the invention described in the following that the movable actuating contacts of all vacuum interrupters of a load selector can be moved only in one direction in order to make or break the electrical contact in the vacuum interrupter.
European Patent Specification EP 1 078 380 B1 describes, by example, a load selector for tapped transformers, wherein several vacuum interrupters are arranged annularly and in the same sense upright on contact supports, since the contact arrangement consists of several tap contacts fixedly arranged in a circle at a cylinder. The contact supports comprise wiper contacts guided by rollers in a diverter ring. The vacuum interrupters are controlled by control cams in this diverter ring (actuating element). In particular, the vacuum interrupters are each controlled by a lower cam track and an upper cam track. The two cam tracks (control cams) are respectively arranged on a concentric circle at the level of the actuating contacts (actuating plungers) of the vacuum interrupters. The two concentric circles lie immediately and directly adjacent to one another so that they together form an upper circular disk in which exclusively the actuating plungers of the vacuum interrupters are disposed. The lower ends of the vacuum interrupters without actuating plungers are disposed opposite on the contact support and form a lower circular disk without actuating contacts. The two circular discs are spaced apart and the middle parts such as, for example, the bellows, of the vacuum interrupters are arranged therebetween.
In CN 101320650 A, CN 101154497 A, DE 2020 1100963 U1, DE 2914928 C2, DE 3833126 A1, WO 2010/142680 A1 and WO 2012/003863 A1 the vacuum interrupters are similarly annularly arranged in the same sense with a control ring that comprises one or two directly and immediately adjacent annular cam tracks.
The vacuum interrupters usually taper in the direction of the actuating elements, whereas they widen in the direction of the opposite ends. The external shape of the vacuum interrupters is thus usually at least approximately conical. A disadvantage of this external shape in load selectors with vacuum interrupters arranged in the same sense is that the oil tank (insulating cylinder, contact cylinder) of the load selector, in which oil tank the vacuum interrupters are arranged in opposite sense, has to have a large diameter so that the load selectors correspondingly are less compact and less space-saving.